417 research outputs found
Vanishing topology of codimension 1 multi-germs over and
We construct all e-codimension 1 multi-germs of analytic (or smooth) maps (kn, T) [rightward arrow] (kp, 0), with n [gt-or-equal, slanted] p − 1, (n, p) nice dimensions, k = or , by augmentation and concatenation operations, starting from mono-germs (|T| = 1) and one 0-dimensional bi-germ. As an application, we prove general statements for multi-germs of corank [less-than-or-eq, slant] 1: every one has a real form with real perturbation carrying the vanishing homology of the complexification, every one is quasihomogeneous, and when n = p − 1 every one has image Milnor number equal to 1 (this last is already known when n [gt-or-equal, slanted] p)
XMM-Newton Observation of the Northwest Radio Relic Region in Abell 3667
Abell 3667 is the archetype of a merging cluster with radio relics. The NW
radio relic is the brightest cluster relic or halo known, and is believed to be
due to a strong merger shock. We have observed the NW relic for 40 ksec of net
XMM time. We observe a global decline of temperature across the relic from 6 to
1 keV, similar to the Suzaku results. Our new observations reveal a sharp
change of both temperature and surface brightness near the position of the
relic. The increased X-ray emission on the relic can be equivalently well
described by either a thermal or nonthermal spectral model. The parameters of
the thermal model are consistent with a Mach number M~2 shock and a shock speed
of ~1200 km s^-1. The energy content of the relativistic particles in the radio
relic can be explained if they are (re)-accelerated by the shock with an
efficiency of ~0.2%. Comparing the limit on the inverse Compton X-ray emission
with the measured radio synchrotron emission, we set a lower limit to the
magnetic field in the relic of 3 muG. If the emission from the relic is
non-thermal, this lower limit is in fact the required magnetic field.Comment: 11 pages, ApJ in pres
On the absence of radio halos in clusters with double relics
Pairs of radio relics are believed to form during cluster mergers, and are
best observed when the merger occurs in the plane of the sky. Mergers can also
produce radio halos, through complex processes likely linked to turbulent
re-acceleration of cosmic-ray electrons. However, only some clusters with
double relics also show a radio halo. Here, we present a novel method to derive
upper limits on the radio halo emission, and analyse archival X-ray Chandra
data, as well as galaxy velocity dispersions and lensing data, in order to
understand the key parameter that switches on radio halo emission. We place
upper limits on the halo power below the
correlation for some clusters, confirming that clusters with double relics have
different radio properties. Computing X-ray morphological indicators, we find
that clusters with double relics are associated with the most disturbed
clusters. We also investigate the role of different mass-ratios and
time-since-merger. Data do not indicate that the merger mass ratio has an
impact on the presence or absence of radio halos (the null hypothesis that the
clusters belong to the same group cannot be rejected). However, the data
suggests that the absence of radio halos could be associated with early and
late mergers, but the sample is too small to perform a statistical test. Our
study is limited by the small number of clusters with double relics. Future
surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to
better address this issue.Comment: 12 pages, 7 figures, MNRAS accepte
GRB 000418: A Hidden Jet Revealed?
We report on optical, near-infrared and centimeter radio observations of
GRB000418 which allow us to follow the evolution of the afterglow from 2 to 200
days after the gamma-ray burst. In modeling these broad-band data, we find that
an isotropic explosion in a constant density medium is unable to simultaneously
fit both the radio and optical data. However, a jet-like outflow with an
opening angle of 10-20 degress provides a good description of the data. The
evidence in favor of a jet interpretation is based on the behavior of the radio
light curves, since the expected jet break is masked at optical wavelengths by
the light of the host galaxy. We also find evidence for extinction, presumably
arising from within the host galaxy, with A(V)=0.4 mag, and host flux densities
of F_R=1.1 uJy and F_K=1.7 uJy. These values supercede previous work on this
burst due to the availability of a broad-band data set allowing a global
fitting approach. A model in which the GRB explodes into a wind-stratified
circumburst medium cannot be ruled out by these data. However, in examining a
sample of other bursts (e.g. GRB990510, GRB000301C) we favor the jet
interpretation for GRB000418.Comment: ApJ, submitte
Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project
We present X-ray and optical analysis of 188 AGN identified from 497 hard
X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra
fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These
medium depth X-ray observations enable us to detect a representative subset of
those sources responsible for the bulk of the 2-8 keV Cosmic X-ray Background.
Brighter than our optical spectroscopic limit, we achieve a reasonable degree
of completeness (77% of X-ray sources with counter-parts r'< 22.5 have been
classified): broad emission line AGN (62%), narrow emission line galaxies
(24%), absorption line galaxies (7%), stars (5%) or clusters (2%). We find that
most X-ray unabsorbed AGN (NH<10^22 cm^-2) have optical properties
characterized by broad emission lines and blue colors, similiar to
optically-selected quasars from the Sloan Digital Sky Survey but with a slighly
broader color distribution. However, we also find a significant population of
redder (g'-i'>1.0) AGN with broad optical emission lines. Most of the X-ray
absorbed AGN (10^22<NH<10^24 cm^-2) are associated with narrow emission line
galaxies, with red optical colors characteristically dominated by luminous,
early type galaxy hosts rather than from dust reddening of an AGN. We also find
a number of atypical AGN; for instance, several luminous AGN show both strong
X-ray absorption (NH>10^22 cm^-2) and broad emission lines. Overall, we find
that 81% of X-ray selected AGN can be easily interpreted in the context of
current AGN unification models. Most of the deviations seem to be due to an
optical contribution from the host galaxies of the low luminosity AGN.Comment: 26 pages; 13 figures (7 color); accepted for publication in the
Astrophysical Journa
Gas Clumping in the Outskirts of Galaxy Clusters, an Assessment of the Sensitivity of STAR-X
In the outskirts of galaxy clusters, entropy profiles measured from X-ray
observations of the hot intracluster medium (ICM) drops off unexpectedly. One
possible explanation for this effect is gas clumping, where pockets of cooler
and denser structures within the ICM are present. Current observatories are
unable to directly detect these hypothetical gas clumps. One of the science
drivers of the proposed STAR-X observatory is to resolve these or similar
structures. Its high spatial resolution, large effective area, and low
instrumental background make STAR-X ideal for directly detecting and
characterizing clumps and diffuse emission in cluster outskirts. The aim of
this work is to simulate observations of clumping in clusters to determine how
well STAR-X will be able to detect clumps, as well as what clumping properties
reproduce observed entropy profiles. This is achieved by using yt, pyXSIM,
SOXS, and other tools to inject ideally modeled clumps into three-dimensional
models derived from actual clusters using their observed profiles from other
X-ray missions. Radial temperature and surface brightness profiles are then
extracted from mock observations using concentric annuli. We find that in
simulated observations for STAR-X, a parameter space of clump properties exists
where gas clumps can be successfully identified using wavdetect and masked, and
are able to recover the true cluster profiles. This demonstrates that STAR-X
could be capable of detecting substructure in the outskirts of nearby clusters
and that the properties of both the outskirts and the clumps will be revealed.Comment: This is a pre-copyedited, author-produced PDF of an article accepted
for publication in RAS Techniques and Instruments (RASTI) following peer
review. The version of record is available online at:
https://academic.oup.com/rasti/article/doi/10.1093/rasti/rzad042/725882
The NuSTAR, XMM-Newton, and Suzaku View of A3395 at the Intercluster Filament Interface
Galaxy clusters are the largest virialized objects in the universe. Their merger dynamics and their interactions with the cosmic filaments that connect them are important for our understanding of the formation of large-scale structure. In addition, cosmic filaments are thought to possess the missing baryons in the universe. Studying the interaction of galaxy clusters and filaments therefore has the potential to unveil the origin of the baryons and the physical processes that occur during merger stages of galaxy clusters. In this paper, we study the connection between A3395 and the intercluster filament with NuSTAR, XMM-Newton, and Suzaku data. Since the NuSTAR observation is moderately contaminated by scattered light, we present a novel technique developed for disentangling this background from the emission from the intracluster medium. We find that the interface of the cluster and the intercluster filament connecting A3395 and A3391 does not show any signs of heated plasma, as was previously thought. This interface has low temperature, high density, and low entropy, thus we suggest that the gas is cooling, being enhanced by the turbulent or tidal "weather"driven during the early stage of the merger. Furthermore, our temperature results from the NuSTAR data are in agreement with those from XMM-Newton and from joint NuSTAR and XMM-Newton analysis for a region with ∼25% scattered light contamination within 1σ. We show that the temperature constraint of the intracluster medium is valid even when the data are contaminated up to ∼25% for ∼5 keV cluster emission
Astro 2020 Science White Paper: Time Domain Studies of Neutron Star and Black Hole Populations: X-ray Identification of Compact Object Types
What are the most important conditions and processes governing the growth of
stellar-origin compact objects? The identification of compact object type as
either black hole (BH) or neutron star (NS) is fundamental to understanding
their formation and evolution. To date, time-domain determination of compact
object type remains a relatively untapped tool. Measurement of orbital periods,
pulsations, and bursts will lead to a revolution in the study of the
demographics of NS and BH populations, linking source phenomena to accretion
and galaxy parameters (e.g., star formation, metallicity). To perform these
measurements over sufficient parameter space, a combination of a wide-field
(>5000 deg^2) transient X-ray monitor over a dynamic energy range (~1-100 keV)
and an X-ray telescope for deep surveys with <5 arcsec PSF half-energy width
(HEW) angular resolution are required. Synergy with multiwavelength data for
characterizing the underlying stellar population will transform our
understanding of the time domain properties of transient sources, helping to
explain details of supernova explosions and gravitational wave event rates.Comment: 9 pages, 2 figures. Submitted to the Astro2020 Decadal Surve
A Hard X-ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR
We present results from sensitive, multi-epoch NuSTAR observations of the
late-type star-forming galaxy M83 (d=4.6 Mpc), which is the first investigation
to spatially resolve the hard (E>10 keV) X-ray emission of this galaxy. The
nuclear region and ~ 20 off-nuclear point sources, including a previously
discovered ultraluminous X-ray (ULX) source, are detected in our NuSTAR
observations. The X-ray hardnesses and luminosities of the majority of the
point sources are consistent with hard X-ray sources resolved in the starburst
galaxy NGC 253. We infer that the hard X-ray emission is most likely dominated
by intermediate accretion state black hole binaries and neutron star low-mass
X-ray binaries (Z-sources). We construct the X-ray binary luminosity function
(XLF) in the NuSTAR band for an extragalactic environment for the first time.
The M83 XLF has a steeper XLF than the X-ray binary XLF in NGC 253, consistent
with previous measurements by Chandra at softer X-ray energies. The NuSTAR
integrated galaxy spectrum of M83 drops quickly above 10 keV, which is also
seen in the starburst galaxies NGC253, NGC 3310 and NGC 3256. The NuSTAR
observations constrain any AGN to be either highly obscured or to have an
extremely low luminosity of 10 erg/s (10-30 keV), implying it
is emitting at a very low Eddington ratio. An X-ray point source consistent
with the location of the nuclear star cluster with an X-ray luminosity of a few
times 10 erg/s may be a low-luminosity AGN but is more consistent with
being an X-ray binary.Comment: Accepted for publication in ApJ (25 pages, 17 figures
The NuSTAR and Chandra View of CL 0217+70 and Its Tell-tale Radio Halo
Mergers of galaxy clusters are the most energetic events in the universe, driving shock and cold fronts, generating turbulence, and accelerating particles that create radio halos and relics. The galaxy cluster CL 0217+70 is a remarkable late-stage merger, with a double peripheral radio relic and a giant radio halo. Chandra detects surface brightness (SB) edges that correspond to radio features within the halo. In this work, we present a study of this cluster with Nuclear Spectroscopic Telescope Array and Chandra data using spectro-imaging methods. The global temperature is found to be kT = 9.1 keV. We set an upper limit for the inverse Compton (IC) flux of ∼2.7 × 10−12 erg s−1 cm−2, and a lower limit to the magnetic field of 0.08 μG. Our local IC search revealed a possibility that IC emission may have a significant contribution at the outskirts of the radio halo emission and on/near shock regions within ∼0.6 r 500 of clusters. We detected a “hot spot” feature in our temperature map coincident with an SB edge, but our investigation on its origin is inconclusive. If the “hot spot” is the downstream of a shock, we set a lower limit of kT > 21 keV to the plasma that corresponds to ∼2. We found three shock fronts within 0.5 r 500. Multiple weak shocks within the cluster center hint at an ongoing merger activity and continued feeding of the giant radio halo. CL 0217+70 is the only example hosting these secondary shocks in multiple form
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